This invention relates to a device for retaining a nuclear fuel rod in a nuclear fuel rod assembly and which allows the rod to be easily removed from the assembly. More specifically, this invention relates to a device for retaining a nuclear fuel rod in a nuclear fuel rod assembly and which allows the rod to be easily removed from the assembly without disturbing any other rods or support elements in the assembly.
Fuel for nuclear reactors is frequently manufactured in the form of elongated fuel rods. In a typical reactor design, fuel rods are arranged in parallel arrays called assemblies. Each assembly is supported in the reactor by a structural cage which allows the entire assembly to be handled together as a unit. Each cage comprises one upper and one lower end fitting at the ends of the assembly and control rods guide tubes extending between the end fittings. The end fittings comprise flat plates called grillages with a plurality of apertures therein, most of which are open to allow for the flow of coolant therethrough and the remainder of which are used to accommodate the ends of the fuel rods and guide tubes. Fastening means at each aperture secure the fuel rods and guide tubes to the grillage. Spacer grids located along the length of the fuel assembly serve to locate and support the fuel rods and guide tubes.
It is often desirable to remove a single fuel rod from an assembly in a nuclear reactor. This may be necessary in order to inspect the rod for research purposes. It would thus be desirable to be able to remove a single fuel rod without disturbing the other rods in the assembly or the end fittings. Also, the fastening means begin to deteriorate upon prolonged thermal stress and irradiation and should not be reused; therefore the fastening means should be removed from the assembly and discarded when a fuel rod is removed. Furthermore, because in the radioactive environment of a nuclear reactor such operations are necessarily performed by remote equipment, it would be desirable to remove both the fuel rod and its associated fastening means in a single operation.
Various attempts have been made to invent alternative types of end fittings to facilitate rod removal. Some of these have incorporated removable plates to allow easy access to an entire fuel rod assembly. Devices of this type include those described in U.S. Pat. No. 3,255,091, entitled "Fuel Arrangement for a Nuclear Reactor" to E. Frisch; U.S. Pat. No. 3,431,170, entitled "Nuclear Reactor Fuel Bundle" to J. L. Lass, et al; and U.S. Pat. No. 3,992,259 entitled, "Fuel Assembly for a Nuclear Reactor" to A. Anthony et al. Other devices have used tubular fittings with pins to retain the rod such as U.S. Pat. No. 3,349,004, entitled "Nuclear Reactor Fuel Bundle" to J. L. Lass et al. Often these devices have several disadvantages: they may require many steps to remove the rod, which makes remote operation difficult, or they may hinder fuel rod growth which normally occurs during irradiation. In addition, use of these devices may structurally weaken the entire fuel assembly.